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Overfertilizing

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Peonies.

Photo: Jardin botanique de Montréal (Gilles Murray)

Fertilizing is useful, but it is important not to go overboard. Although you may be tempted to exceed the recommended application rate in the hope that it will make your plants grow better, it is important not to do so. When the concentration of fertilizer in the soil is too high, it is difficult for plants to absorb water and they will eventually decline.

Overfertilizing also causes plants to grow too quickly and too lushly. This type of growth makes them vulnerable to insect pests and diseases. This is a common problem when high-nitrogen fertilizers are used.

Overfertilizing can also cause plant deficiencies. For instance, excess potassium in the soil interferes with the assimilation of magnesium, even when it is present in sufficient quantities in the soil. The plant will end up lacking magnesium and showing symptoms of a deficiency.

Overfertilizing also interferes with biological activity in the soil. Mycorrhizal fungi, for instance, are very sensitive to overfeeding, especially with phosphorous.

Finally, remember that excess nutrients leached from the soil pollute the environment, particularly sources of drinking water. This is another reason why it is important to use fertilizers in moderation.